Phenol is one of the most important chemical intermediates, reflecting primarily its high-volume use in resin manufacture. Principal end products comprise phenolic resins, principally phenol-formaldehyde resins used in the construction, appliance and automotive industries, and Bisphenol A for epoxy and polycarbonate resins. A significant proportion of the phenol produced is used to produce alkylphenols, which are converted to nonionic surfactants, resins and modifiers, agrochemicals and pharmaceuticals.
The dominant process for production of phenol proceeds via cumene and cumene hydroperoxide. Benzene and propylene are alkylated to obtain cumene, which in turn is oxidized to form cumene hydroperoxide. The hydroperoxide is cleaved using an acid catalyst to form phenol and acetone. The economics of phenol production by the cumene route are highly favorable compared to older processes, leading to the dominance of this route. Essentially one mole of acetone is produced for each mole of phenol, however, leading to an undesirable rigidity in product structure.
Phenol via toluene oxidation was developed by Dow, DSM and others to overcome the byproduct issue associated with the cumene route, but the inherent yield loss and expensive materials of construction prevented this route from making strong inroads. Older processes such as sulfonation, chlorobenzene, and the Raschig Hooker process convened benzene without substantial hydrocarbon byproducts but were burdened by such disadvantages of high chemical and energy consumption, corrosion, and the need for catalyst regeneration. The Scientific Design cyclohexanone/cyclohexanol route was not economic for phenol alone due to a phenol/cyclohexanone azeotrope.
A problem facing workers in the field of phenol technology, therefore, is to develop an economically attractive route for phenol production which avoids the byproduct, corrosion and operating-cost disadvantages of earlier processes.
Nemeth et al. teach a process for the direct hydroxylation of aromatic compounds using hydrogen peroxide in U.S. Pat. No. 5,233,097. Using a titanoaluminosilicate molecular sieve, the process achieves high product selectivity using relatively dilute hydrogen peroxide solutions; the state of the art based on titanosilicate catalysts and types of hydrogen peroxide solutions is discussed extensively. An earlier process for the direct hydroxylation of aromatics with hydrogen peroxide using a hydrogen fluoride--carbon dioxide complex is disclosed in U.S. Pat. No. 3,453,332 (Vesely et al.).
Production of the benzene feedstock for direct oxidation has not been related to a phenol-production scheme, but a variety of processes are available to obtain benzene. In addition to conventional catalytic reforming. U.S. Pat. No. 5,211,837 teaches processing with a sulfur-sensitive L-zeolite catalyst that favors benzene production from lighter naphtha feedstocks. U.S. Pat. No. 5,258,563 discloses production of benzene in high yields from light aliphatic hydrocarbons.
Phenol from cumene nevertheless remains the process of choice for commercial installations in spite of the issue of byproduct acetone; direct conversion of benzene to phenol has not become economically attractive based on the teachings of the art.